What's the difference between reams and sheets?

A ream is a paper-related term and means a specific quantity of the paper in question. When purchasing a blank paper, a ream is 500 sheets. However, other quantities can be specified (i.e. reams of 250, 100, etc.). Sheets indicated that the wrapping paper will be delivered in sheets cut to the indicated size, rather than in rolls of fixed widths, allowing for standardization and quicker packaging (as the sheets will always be the same size and will not need to be cut)